Food allergy
It is estimated that nearly 4% of the paediatric population worldwide have a diagnosis of food allergy.
The diagnosis of food allergy is based on detailed history of the symptoms and is confirmed or denied with the aid of skin prick tests and specific IgEs where indicated. The interpretation of investigations can be tricky particularly in an atopic child where other causes of atopy can lead to false positive blood results. Same with skin prick tests there are limitations and doing tests blindly in order to ‘’fish’’ a cause of symptoms is not useful as there can also be false positive results due to sensitisation and not clinical allergy.
The gold standard for diagnosis of food allergy is double blind food challenge where both the patient and the clinician are not aware if the food provided contains the alleged food or is a placebo. However, this is mainly reserved for research purposes and in clinical practice we proceed with an open food challenge where indicated and safe to do so. During that process a child is advised either at home or in a supervised clinical environment to try the alleged food in increments and will observed for symptoms. This is a common process to introduce food previously avoided where there is suspected clinical history but investigations did not show sensitisation.
Previously the mainstay of management has been avoidance whereas now we try to delabel as much as possible or at least introduce cooked form eg of milk or egg into the child’ diet with the hope they will maintain some tolerance. Tests will be periodically repeated to assess level of sensitisation and work further on introduction of the alleged food or continue with avoidance.
My role is to assess whether your child has true food allergy as there are other conditions like viral illnesses, contact dermatitis, eczema flares and in infants colics and reflux that mimic food allergy. Whether we proceed or not to do further tests depends on the type of suspected food allergy. There are mainly two typeds of food allergy:
- Immediate (igE mediated) food allergy where symptoms present from minutes-2 hours from ingestion. Main symptoms affect the skin, gut and less frequently can cause anaphylaxis where respiratory of cardiovascular systems can be affected. In this type of food allergy we can proceed to skin prick and/or blood tests to support or refute the diagnosis.
- Delayed (non IgE mediated) food allergy where symptoms present between 2-72 hours and mainly involve eczema flare, gut symptoms, blood in the stools. This is common presentation of milk and/or egg allergy in infants that suffer from colics and/or reflux and/or eczema. The diagnosis is based on food avoidance for 4-6 weeks and slow reintroduction of the alleged food. If symptoms resolve during the period of avoidance and relapse during reintroduction this confirms the diagnosis. The skin prick and blood tests are of no use in this type of food allergy.
Making the correct diagnosis of milk allergy in infants can be challenging as there are many symptoms that mimic milk allergy and lead to unnecessary dairy avoidance with increasing restrictions during weaning.
Although we discussed about every effort put to de-label a suspected food allergy where possible, at the same time we will put every effort to safeguard your child from future reactions. During your visit we will discuss avoidance measures, eating out, emergency kits and I will issue adrenaline autoinjector where indicated. We will also explore groups of food that cross-react and need to be assessed if not already part of the normal diet.
Regarding prognosis of food allergy , there are types of food allergy that children outgrow and others that continue for a lifetime:
- Milk: The prognosis for outgrowing a milk allergy is very positive, but research does suggest that the age this happens at, varies. In the last 10 years, there has been a shift towards tolerating milk at a later age. In the CoFAR and Europrevall studies, 53% of children outgrew their allergy by two years of age, and 57% outgrew their allergy at one year. However, as with the egg allergy, some studies have shown a slower rate of achieving tolerance, with one reporting that 19% outgrew their cow’s milk allergy at age 4, 42% at age 8, 64% at age 12, and 79% at age 16.
- Soy, Eggs, and Wheat. A whopping 80 to 95 percent of children outgrow their milk, soy, egg, and/or wheat allergies by age 5.
- Sesame. Sesame allergy seems to appear early in life, and according to one study persists for 80 % of children. If they were to outgrow sesame allergy, they typically do so by approximately 6 years of age.
- Peanuts, Tree Nuts, Fish, and Shellfish. In 80 to 90 percent of cases, allergies to peanuts, tree nuts (almond, walnut, pecan, cashew, pistachio, Brazil nut, macademia) fish, and shellfish are lifelong.
References:
- Anaphylaxis UK, Outgrowing food allergy.
- BSACI guideline for the diagnosis and management of cow’s milk allergy.
